Its often difficult on large projects to keep track of all the additions as a system grows. When a project grows, it gets more difficult to keep all system drawings accurate and correct. If a drawing isn't automatically generated, then you can have little faith that it is absolutely up-to-date.
The alternative is to write tools that examine the code and draw representations of the systems continuously. This can be part of a nightly build, or a tool that can be run on-demand in order to make better decisions, resolve design issues early, and identify impact of changes.
In this instance I was having trouble keeping up with what Web Services we had; What Stored Procedures they relied upon, and what SQL Server tables those Stored Procedures depended upon.
The application we wrote in a couple of days simply hunts through all *.cs files and uses Regular Expressions to find applicable code. It then uses Microsoft Research's Graph Drawing Tool "GLEE" to visually represent it. GLEE is incredibly easy to use and integrate. The following screen-shot (with the sensitive names removed) took less than 15 lines of code to produce (and a few hundred to do the Regular Expression hunting).
A side-benefit of this tool is that it forces the team to conform to the coding standards. If they want their new code to be incorporated into the latest drawings, follow the patterns provided.
Its great to come into work each morning and see what has been added, and to ensure that the cross-coupling even at the database level isn't going to cause use duress later in the project. We can quickly see what a DB schema change will impact. Sleeping much better now....